What is not standardized (or rather: even similar) is the signage delimiting settlement from rural area.

You've to check that for the countries in question. For MNE this is on
https://en.wikipedia.org/wiki/Road_s...ormation_signs III-29 through III-32

(it's often black on yellow/orange-ish - but for stark contrast see e.g. France https://en.wikipedia.org/wiki/Road_s...Location_signs )